zstd/tests/fuzz/fuzz_helpers.c
Nick Terrell 5717bd39ee [lib] Fix NULL pointer dereference
When the output buffer is `NULL` with size 0, but the frame content size
is non-zero, we will write to the NULL pointer because our bounds check
underflowed.

This was exposed by a recent PR that allowed an empty frame into the
single-pass shortcut in streaming mode.

* Fix the bug.
* Fix another NULL dereference in zstd-v1.
* Overflow checks in 32-bit mode.
* Add a dedicated test.
* Expose the bug in the dedicated simple_decompress fuzzer.
* Switch all mallocs in fuzzers to return NULL for size=0.
* Fix a new timeout in a fuzzer.

Neither clang nor gcc show a decompression speed regression on x86-64.
On x86-32 clang is slightly positive and gcc loses 2.5% of speed.

Credit to OSS-Fuzz.
2020-05-06 12:09:02 -07:00

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C

/*
* Copyright (c) 2016-2020, Facebook, Inc.
* All rights reserved.
*
* This source code is licensed under both the BSD-style license (found in the
* LICENSE file in the root directory of this source tree) and the GPLv2 (found
* in the COPYING file in the root directory of this source tree).
* You may select, at your option, one of the above-listed licenses.
*/
#include "fuzz_helpers.h"
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
void* FUZZ_malloc(size_t size)
{
if (size > 0) {
void* const mem = malloc(size);
FUZZ_ASSERT(mem);
return mem;
}
return NULL;
}
int FUZZ_memcmp(void const* lhs, void const* rhs, size_t size)
{
if (size == 0) {
return 0;
}
return memcmp(lhs, rhs, size);
}